CN116827438A - Optical communication system and first node - Google Patents
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- CN116827438A CN116827438A CN202210275920.9A CN202210275920A CN116827438A CN 116827438 A CN116827438 A CN 116827438A CN 202210275920 A CN202210275920 A CN 202210275920A CN 116827438 A CN116827438 A CN 116827438A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
- H04B10/2543—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to fibre non-linearities, e.g. Kerr effect
- H04B10/2563—Four-wave mixing [FWM]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
- H04J14/02—Wavelength-division multiplex systems
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Abstract
An optical communication system and a first node are used for solving the problem of four-wave mixing of the optical communication system in the prior art. The method can be applied to a forward communication system or other possible single-fiber bidirectional transmission systems and the like. The optical communication system comprises a first node, a second node and an optical fiber for connecting the first node and the second node, wherein the optical fiber is used for transmitting N first-direction wavelength channels sent by the first node to the second node and N second-direction wavelength channels sent by the second node to the first node, and N is an integer larger than 2. The zero dispersion wavelength ZDW of the optical fiber belongs to a ZDW area, at least two first direction wavelength channels and at least one second direction wavelength channel are positioned in the ZDW area, or at least two second direction wavelength channels and at least one first direction wavelength channel are positioned in the ZDW area, and the four-wave mixing effect of the optical fiber can be weakened or restrained by mixing the first direction wavelength channels and the second direction wavelength channels distributed in the ZDW area.
Description
Technical Field
The present application relates to the field of optical communications technologies, and in particular, to an optical communications system and a first node.
Background
With the rapid growth of communication services and the number of users, optical communication technologies have been rapidly developed. Wavelength division multiplexing (wavelength division multiplexing, WDM) transmission technology is a relatively efficient way to achieve upgrades and expansion of optical communication systems. Optical fibers are commonly used in optical communication systems to transmit optical signals, but the presence of zero dispersion wavelengths (zero-dispersion wavelength, ZDW) or zero dispersion frequencies (zero-dispersion frequency, ZDF) in the optical fibers, and the presence of severe four-wave mixing of optical signals transmitted around the ZDW (or ZDF) and around the ZDW (or ZDF), can result in distortion of the transmitted optical signals, which can reduce the performance of the optical communication system. The zero dispersion wavelength is the group velocity dispersion (or called group delay dispersion or second order dispersion of unit length) of the optical fiber at this wavelength, and the group velocity dispersion is a phenomenon that the group velocity of light in the transparent medium is related to the frequency or wavelength of light, zdf=c/ZDW, and C is the light velocity.
Currently, in order to suppress four-wave mixing in an optical fiber, the following methods are generally adopted: the transmission power of the light source transmitting the optical signal is reduced. Based on this approach, part of the four-wave mixing can be attenuated, but the power margin of the optical signal is also suppressed, and for transmissions that are far away, there is still a severe four-wave mixing effect (or called four-wave mixing impairment) in this way.
In summary, how to reduce or suppress the four-wave mixing effect in an optical communication system is a technical problem that needs to be solved currently.
Disclosure of Invention
The application provides an optical communication system and a first node, which are used for weakening or inhibiting four-wave mixing of an optical fiber.
In a first aspect, the present application provides an optical communication system comprising a first node, a second node, and an optical fiber for connecting the first node and the second node, the ZDW of the optical fiber belonging to a ZDF area, or it can be understood that the ZDF of the optical fiber belongs to a ZDF area, wherein zdf=c/ZDW, C is the speed of light. The optical fiber is used for transmitting N first-direction wavelength channels and N second-direction wavelength channels, N is an integer greater than 2, at least two first-direction wavelength channels and at least one second-direction wavelength channel are located in a ZDW area, or at least two second-direction wavelength channels and at least one first-direction wavelength channel are located in the ZDW area, the first-direction wavelength channels and the second-direction wavelength channels in the ZDW area are distributed in a mixed mode, the first-direction wavelength channels are wavelength channels sent from a first node to a second node, and the second-direction wavelength channels are wavelength channels sent from the second node to the first node.
The first direction wavelength channels and the second direction wavelength channels in the ZDW region are mixed and distributed, which is also understood that the number of consecutively adjacent first direction wavelength channels in the ZDW region is less than or equal to 2, and the number of consecutively adjacent second direction wavelength channels in the ZDW region is less than or equal to 2.
Based on the scheme, in the ZDW region, the first-direction wavelength channels and the second-direction wavelength channels are mixed and distributed, so that the interval between the wavelength channels transmitted in the same direction (namely, the first-direction wavelength channels or the second-direction wavelength channels) is increased; on the other hand, the method helps to reduce the number of forming four-wave mixing or can eliminate the four-wave mixing, taking the first-direction wavelength channels as an example, for example, 3 groups of first-direction wavelength channels can form four-wave mixing based on the prior art distribution mode, but based on the scheme of the application, at most 2 groups of first-direction wavelength channels can form four-wave mixing; therefore, based on the above-described scheme, it is helpful to reduce or suppress the four-wave mixing effect, so that the degradation of the performance of the optical communication system due to the four-wave mixing can be suppressed.
In one possible implementation, the ZDWs of different fibers may be different, with the ZDW region to which the ZDW of a standard single-mode fiber belongs ranging from [1300 nm, 1324 nm ].
In one possible implementation, the N first direction wavelength channels and the N second direction wavelength channels are distributed to satisfy any one or more of the following: among the N first-direction wavelength channels, the centers of the four symmetrical first-direction wavelength channels are not located in the ZDW region; further, among the N second-direction wavelength channels, there are no four symmetrical second-direction wavelength channels whose centers are located in the ZDW region.
By designing N first-direction wavelength channels such that there are no four symmetric first-direction wavelength channels centered in the ZDW region, it is helpful to attenuate or suppress the first-direction wavelength channels from generating non-degenerate four-wave mixing (see explanation at the following expression); by designing the N second-direction wavelength channels such that the centers of the four symmetrical second-direction wavelength channels are not located in the ZDW region, the second-direction wavelength channels can be reduced or suppressed from generating nondegenerate four-wave mixing.
In one possible implementation, the N first direction wavelength channels and the N second direction wavelength channels are distributed to satisfy any one or more of the following: among the N first-direction wavelength channels, there are no three first-direction wavelength channels which are equally spaced and at least two of which are located in the ZDW region; further, among the N second-direction wavelength channels, there are no third second-direction wavelength channels which are equally spaced and at least two of which are located in the ZDW region.
By designing N first-direction wavelength channels, there are no three first-direction wavelength channels that are equally spaced and at least two of which are located in the ZDW region, it is helpful to attenuate or suppress the first-direction wavelength channels from producing degenerate four-wave mixing (see explanation at the following terminology); by designing the N second-direction wavelength channels such that there are no three second-direction wavelength channels that are equally spaced and at least two of which are located in the ZDW region, the second-direction wavelength channels can be attenuated or suppressed to produce non-degenerate four-wave mixing.
To ensure proper transmission of wavelength channels in an optical fiber, the spacing of the wavelength channels needs to be controlled. If the wavelength interval is too small, mutual interference is easily caused, and if the wavelength interval is too large, the utilization of the optical fiber is reduced. In one possible implementation, the minimum frequency separation of the N first direction wavelength channels and the N second direction wavelength channels of the hybrid distribution is equal to 800 gigahertz (GHz). In other words, the minimum frequency spacing of 2N wavelength channels (including N first direction wavelength channels and N second direction wavelength channels) is about 800GHz. The spacing between wavelength channels may be characterized by frequency spacing, or alternatively by wavelength spacing, as exemplified herein by frequency spacing.
In another possible implementation, the minimum frequency separation of the N first direction wavelength channels and the N second direction wavelength channels of the hybrid distribution is equal to 400GHz.
By setting the minimum frequency interval to 400GHz, normal transmission of the wavelength channel in the optical fiber can be ensured, and the wave band can be fully utilized, so that the transmission capacity of the optical fiber can be improved, and the utilization efficiency of optical fiber resources can be improved.
The following exemplarily shows 4 arrangements of N first direction wavelength channels and N second direction wavelength channels, and each of these 4 arrangements may achieve attenuation or suppression of the four-wave mixing effect of the optical fiber.
Scheme 1, N first-direction wavelength channels alternate with N second-direction wavelength channels (or are referred to as cross-distribution).
In one possible implementation, the N first direction wavelength channels are equally spaced, and the N second direction wavelength channels are equally spaced. Further, the first direction wavelength channels are spaced apart by the same wavelength as the second direction wavelength channels.
As an example, n=6, and N first direction wavelength channels and N second direction wavelength channels are distributed in order from small to large: the first direction wavelength channel, the second direction wavelength channel, the first direction wavelength channel, the second direction wavelength channel. It is also understood that the 12 wavelength channels are in order of small arrival of wavelengths: the 1 st is the first direction wavelength channel, the 2 nd is the second direction wavelength channel, the 3 rd is the first direction wavelength channel, the 4 th is the second direction wavelength channel, the 5 th is the first direction wavelength channel, the 6 th is the second direction wavelength channel, the 7 th is the first direction wavelength channel, the 8 th is the second direction wavelength channel, the 9 th is the first direction wavelength channel, the 10 th is the second direction wavelength channel, the 11 th is the first direction wavelength channel, the 12 th is the second direction wavelength channel.
Alternatively, the N first direction wavelength channels and the N second direction wavelength channels are distributed in order of the wavelengths from small to large: the second direction wavelength channel, the first direction wavelength channel, the second direction wavelength channel, the first direction wavelength channel. In other words, the 12 wavelength channels are in order of small arrival of wavelengths: the 1 st is the second direction wavelength channel, the 2 nd is the first direction wavelength channel, the 3 rd is the second direction wavelength channel, the 4 th is the first direction wavelength channel, the 5 th is the second direction wavelength channel, the 6 th is the first direction wavelength channel, the 7 th is the second direction wavelength channel, the 8 th is the first direction wavelength channel, the 9 th is the second direction wavelength channel, the 10 th is the first direction wavelength channel, the 11 th is the second direction wavelength channel, the 12 th is the first direction wavelength channel.
Based on the above scheme 1, the intervals of the N first-direction wavelength channels transmitted in the same direction are increased, so that the four-wave mixing effect caused by the N first-direction wavelength channels is reduced. Similarly, the interval between N second direction wavelength channels transmitted in the same direction is increased, so that four-wave mixing caused by the N second direction wavelength channels is reduced.
In one possible implementation, the wavelength intervals of the N first direction wavelength channels are different, and/or the wavelength intervals of the N second direction wavelength channels are different. Based on this, three possible schemes are shown below, namely scheme 2, scheme 3 and scheme 4, by way of example.
The four-wave mixing effect of the optical fiber is further weakened by designing that the wavelength intervals of the N first-direction wavelength channels are different and/or the wavelength intervals of the N second-direction wavelength channels are different.
Scheme 2, the order of the pair of wavelength channels in scheme 1 is interchanged.
As an example, n=6, the N first direction wavelength channels and N second direction wavelength channels are distributed in order of the wavelengths from small to large: a first direction wavelength channel, a second direction wavelength channel, a first direction wavelength channel a second direction wavelength channel, a first direction wavelength channel, a second direction wavelength channel the second direction wavelength channel, the first direction wavelength channel, the second direction wavelength channel. It is also understood that the 1 st, 2 nd, 3 rd, 4 th, 5 th, 6 th, 7 th, 8 th, 9 th, 10 th, 11 th, and 12 th first, second direction wavelength channels.
Alternatively, taking n=6 as an example, the N first direction wavelength channels and the N second direction wavelength channels are distributed in order of the wavelengths from small to large: a second direction wavelength channel, a first direction wavelength channel, a second direction wavelength channel, a first direction wavelength channel the first direction wavelength channel, the second direction wavelength channel, the first direction wavelength channel. Alternatively, it is also understood that the 1 st is the second direction wavelength channel, the 2 nd is the first direction wavelength channel, the 3 rd is the second direction wavelength channel, the 4 th is the first direction wavelength channel, the 5 th is the second direction wavelength channel, the 6 th is the first direction wavelength channel, the 7 th is the first direction wavelength channel, the 8 th is the second direction wavelength channel, the 9 th is the second direction wavelength channel, the 10 th is the first direction wavelength channel, the 11 th is the second direction wavelength channel, and the 12 th is the first direction wavelength channel.
Scheme 3, the order of the two pairs of wavelength channels in scheme 1 above is interchanged.
Taking n=6 as an example, the N first direction wavelength channels and the N second direction wavelength channels are distributed in order of the wavelengths from small to large: the first direction wavelength channel, the second direction wavelength channel, the first direction wavelength channel, the second direction wavelength channel, the first direction wavelength channel, the second direction wavelength channel. It is also understood that the 1 st, 2 nd, 3 rd, 4 th, 5 th, 6 th, 7 th, 8 th, 9 th, 10 th, 11 th, and 12 th first, second direction wavelength channels.
Alternatively, the N first direction wavelength channels and the N second direction wavelength channels are distributed in order of the wavelengths from small to large: the second direction wavelength channel, the first direction wavelength channel, the second direction wavelength channel, the first direction wavelength channel. It is also understood that the 1 st is the second direction wavelength channel, the 2 nd is the first direction wavelength channel, the 3 rd is the first direction wavelength channel, the 4 th is the second direction wavelength channel, the 5 th is the second direction wavelength channel, the 6 th is the first direction wavelength channel, the 7 th is the second direction wavelength channel, the 8 th is the first direction wavelength channel, the 9 th is the first direction wavelength channel, the 10 th is the second direction wavelength channel, the 11 th is the second direction wavelength channel, the 12 th is the first direction wavelength channel.
Scheme 4, the order of the three pairs of wavelength channels in scheme 1 above is interchanged.
Taking n=6 as an example, the N first direction wavelength channels and the N second direction wavelength channels are distributed in order of the wavelengths from small to large: the first direction wavelength channel, the second direction wavelength channel, the first direction wavelength channel. It is also understood that the 1 st, 2 nd, 3 rd, 4 th, 5 th, 6 th, 7 th, 8 th, 9 th, 10 th, 11 th, and 12 th first direction wavelength channels are first direction wavelength channels, second direction wavelength channels, respectively.
Alternatively, the N first direction wavelength channels and the N second direction wavelength channels are distributed in order of the wavelengths from small to large: the second direction wavelength channel, the first direction wavelength channel, the second direction wavelength channel. It is also understood that the 1 st is the second direction wavelength channel, the 2 nd is the first direction wavelength channel, the 3 rd is the first direction wavelength channel, the 4 th is the second direction wavelength channel, the 5 th is the first direction wavelength channel, the 6 th is the second direction wavelength channel, the 7 th is the second direction wavelength channel, the 8 th is the first direction wavelength channel, the 9 th is the first direction wavelength channel, the 10 th is the second direction wavelength channel, the 11 th is the first direction wavelength channel, the 12 th is the second direction wavelength channel.
If the 5 wavelength channels with the longest wavelength among the 12 wavelength channels are located in the ZDW region, the distribution of the 6 first direction wavelength channels in the above schemes 2, 3 and 4 satisfies: the center of the four symmetrical first-direction wavelength-channels that are not present in the 6 first-direction wavelength-channels is located in the ZDW region, and the four first-direction wavelength-channels that are not present in the 6 first-direction wavelength-channels: three wavelength channels in the first direction are equally spaced and at least two of the three are located in the ZDW region. The distribution of the 6 wavelength channels in the second direction satisfies the following conditions: the center of the second direction wavelength channels in which four symmetry second direction wavelength channels are not present in the 6 second direction wavelength channels is located in the ZDW region, and the second direction wavelength channels in which three intervals are identical and at least two of which are located in the ZDW region are not present in the 6 second direction wavelength channels. Therefore, based on the above-described schemes 2, 3 and 4, four-wave mixing of the optical fiber is facilitated to be reduced or suppressed.
In one possible implementation, the first node includes N first optical transceivers and one first combiner/demultiplexer, and the second node includes N second optical transceivers and one second combiner/demultiplexer; the first end of the first multiplexer/demultiplexer is connected with N first optical transceivers, and the second end of the first multiplexer/demultiplexer is connected with optical fibers between the first node and the second node; the first end of the second multiplexer/demultiplexer is connected with the N second optical transceivers, and the second end of the second multiplexer/demultiplexer is connected with the optical fibers between the first node and the second node.
In one possible implementation, the number of ports at the first end and the second end of the first combiner/divider is N:1, the number of ports at the first end and the second end of the second multiplexer/demultiplexer is N:1.
2N wavelength channels (including N first direction wavelength channels and N second direction wavelength channels) are transmitted through N ports of one combiner/demultiplexer (including a first combiner/demultiplexer and a second combiner/demultiplexer), which is helpful for saving 50% of ports of the combiner/demultiplexer.
In one possible implementation, a first optical transceiver corresponds to a first directional wavelength channel and a second directional wavelength channel, adjacent to the first directional wavelength channel and the second directional wavelength channel corresponding to the same first optical transceiver; and/or, a second optical transceiver corresponds to a first direction wavelength channel and a second direction wavelength channel, and is adjacent to the first direction wavelength channel and the second direction wavelength channel corresponding to the same second optical transceiver. That is, the N first optical transceivers and the N second optical transceivers may implement transmitting 2N wavelength channels (including N first direction wavelength channels and N second direction wavelength channels).
The number of first optical transceivers and/or the number of second optical transceivers included in the optical communication system can be reduced by the adjacent first-direction wavelength channels and second-direction wavelength channels corresponding to the same first optical transceiver and/or the adjacent first-direction wavelength channels and second-direction wavelength channels corresponding to the same second optical transceiver.
In one possible implementation, the first optical transceiver comprises a first fiber optic circulator and the second optical transceiver comprises a second fiber optic circulator.
Because the structure of the optical fiber circulator is simpler, the optical fiber circulator is used as an optical transceiver, and the size of an optical communication system is reduced.
In one possible implementation, the first node comprises a Distribution Unit (DU) and/or a Central Unit (CU), and the second node comprises an active antenna unit (active antenna unit, AAU).
In a second aspect, the present application provides a first node, the first node comprising N first optical transceivers, the N first optical transceivers being configured to transmit N first direction wavelength channels and to receive N second direction wavelength channels, N being an integer greater than 2; the N first-direction wavelength channels and the N second-direction wavelength channels are transmitted through the optical fiber, the ZDW of the optical fiber belongs to a ZDW area, at least two first-direction wavelength channels or at least two second-direction wavelength channels are located in the ZDW area, the first-direction wavelength channels and the second-direction wavelength channels in the ZDW area are mixed and distributed, the first-direction wavelength channels are wavelength channels sent from a first node to a second node, and the second-direction wavelength channels are wavelength channels sent from the second node to the first node.
In one possible implementation, the first node further includes a first combiner/divider, a first end of the first combiner/divider being connected to the N first optical transceivers, and a second end of the first combiner/divider being configured to be connected to an optical fiber.
In one possible implementation, one first optical transceiver corresponds to one first direction wavelength channel and one second direction wavelength channel, adjacent to the first direction wavelength channel and the second direction wavelength channel corresponding to the same first optical transceiver.
In one possible implementation, the first optical transceiver comprises a first fiber circulator.
In one possible implementation, the number of ports at the first end and the second end of the first combiner/divider is N:1.
in a third aspect, the present application provides a second node comprising N second optical transceivers for receiving N first direction wavelength channels and for transmitting N second direction wavelength channels, N being an integer greater than 2; the N first-direction wavelength channels and the N second-direction wavelength channels are transmitted through the optical fiber, the ZDW of the optical fiber belongs to a ZDW area, at least two first-direction wavelength channels or at least two second-direction wavelength channels are located in the ZDW area, the first-direction wavelength channels and the second-direction wavelength channels in the ZDW area are mixed and distributed, the first-direction wavelength channels are wavelength channels sent from a first node to a second node, and the second-direction wavelength channels are wavelength channels sent from the second node to the first node.
In one possible implementation, the second node further includes a second combiner/divider, a first end of the second combiner/divider is connected to the N second optical transceivers, and a second end of the second combiner/divider is connected to the optical fiber.
In one possible implementation, one second optical transceiver corresponds to one first direction wavelength channel and one second direction wavelength channel, adjacent to the first direction wavelength channel and the second direction wavelength channel corresponding to the same second optical transceiver.
In one possible implementation, the second optical transceiver comprises a second fiber circulator.
In one possible implementation, the number of ports at the first end and the second end of the second multiplexer/demultiplexer is N:1.
the technical effects achieved by any one of the second aspect to the third aspect may be referred to the description of the beneficial effects in the first aspect, and the detailed description is not repeated here.
Drawings
FIG. 1a is a schematic diagram of a non-degenerate four-wave mixer according to the present application;
FIG. 1b is a schematic diagram of a degenerate four-wave mixer provided by the present application;
fig. 2a is a schematic diagram of a possible application scenario provided by the present application;
fig. 2b is a schematic diagram of another possible application scenario provided by the present application;
FIG. 3 is a schematic diagram of a wavelength channel distribution according to the present application;
FIG. 4 is a schematic diagram of another method for generating four-wave mixing according to the present application;
fig. 5 is a schematic diagram of an architecture of an optical communication system according to the present application;
FIG. 6a is a schematic diagram illustrating a distribution of wavelength channels according to the present application;
FIG. 6b is a schematic diagram showing a distribution of wavelength channels according to another embodiment of the present application;
FIG. 7a is a schematic diagram showing a distribution of wavelength channels according to another embodiment of the present application;
FIG. 7b is a schematic diagram showing a distribution of wavelength channels according to another embodiment of the present application;
FIG. 8a is a schematic diagram showing a distribution of wavelength channels according to another embodiment of the present application;
FIG. 8b is a schematic diagram showing a distribution of wavelength channels according to another embodiment of the present application;
FIG. 9a is a schematic diagram showing a distribution of wavelength channels according to another embodiment of the present application;
FIG. 9b is a schematic diagram showing a distribution of wavelength channels according to another embodiment of the present application;
fig. 10 is a schematic diagram of a connection relationship between a first node and a second node according to the present application;
FIG. 11 is a schematic view of an optical fiber circulator according to the present application;
fig. 12 is a schematic diagram of a connection relationship between a first fiber circulator and a second fiber circulator according to the present application.
Detailed Description
Embodiments of the present application will be described in detail below with reference to the accompanying drawings.
Hereinafter, some terms in the present application will be explained. It should be noted that these explanations are for the convenience of those skilled in the art, and do not limit the scope of the present application.
1. Four-wave mixing (FWM)
Four-wave mixing is based on three-order optical nonlinearity (X (3) Coefficient description). Four-wave mixing may occur when at least two different frequencies (or wavelengths) of light are propagating in a nonlinear medium, such as an optical fiber. Referring to FIG. 1a, v is two frequencies 1 And v 2 (v 2 >v 1 ) For example, due to the presence of refractive index modulation of the difference frequency, two new frequencies are generated, respectively: v 3 ＝v 1 -(v 2 -v 1 )＝2v 1 -v 2 And v 4 ＝v 2 +(v 2 -v 1 )＝2v 2 -v 1 . Thus, if it is originally present at a frequency v 3 Or v 4 Is expressed as a frequency v 3 And v 4 Amplified, i.e. the light of these two frequencies undergoes parametric amplification, thereby amplifying the original frequency v 3 Or v 4 Is influenced and disturbed.
When the four-wave mixing effect involves four different frequencies (or wavelengths), it is referred to as nondegenerate four-wave mixing (or nondegenerate four-wave mixing), see fig. 1a. When two frequencies of the four frequencies involved in the four-wave mixing are coincident, it is called degenerate four-wave mixing, see fig. 1b.
The four-wave mixing effect is often detrimental in fiber optic communications, particularly in wavelength division multiplexing techniques, where it can cause crosstalk between different wavelength channels and/or imbalance in channel power.
2. Single mode optical fiber
Single mode fiber refers to an optical fiber that supports only one propagation mode (i.e., self-consistent electric field distribution in the fiber) per polarization direction for a given wavelength. Typically with a relatively small core (e.g., a few microns in diameter) and a small refractive index difference between the core and the cladding. The mode radius (typically characterized by the lateral extent of the optical intensity distribution) is typically a few micrometers (um).
3. O-band
Not all wavelengths of light are suitable for optical fiber communications. The wavelengths of light are different and the transmission losses in the optical fibers are different. Generally, light in the low-loss wavelength region (1260 nm to 1625 nm) is suitable for optical fiber communication. The light of the low loss wavelength region may be further divided into five bands, respectively referred to as O band (1260 nm to 1360 nm), E band (1360 nm to 1460), S band (1460 nm to 1530 nm), C band (1530 nm to 1565 nm) and L band (1565 nm to 1625 nm).
Because standard single-mode optical fibers have lower dispersion, minimum signal distortion and lower loss in the O band, the nonlinearity of the standard single-mode optical fibers is difficult to control, and some wavelengths can generate obvious four-wave mixing effect near the ZDW of the optical fibers.
4. Wavelength division multiplexing (wavelength division multiplexing, WDM)
Wavelength division multiplexing refers to a technology of converging two or more kinds of light with different wavelengths (carrying various information) at a transmitting end through a multiplexer (also called a multiplexer), and coupling the two or more kinds of light into the same optical fiber for transmission; at the receiving end, the light of various wavelengths is separated by a demultiplexer (also known as a demultiplexer or demultiplexer) and then further processed by an optical receiver to recover the original signal. This technique of transmitting two or more different wavelengths of light simultaneously in the same optical fiber is called wavelength division multiplexing. The transmission capacity of the optical fiber can be improved by the wavelength division multiplexing technology.
5. Wavelength channel
An optical carrier of a given wavelength may be referred to as a wavelength channel after it carries a signal. The wavelengths of the optical carriers of different wavelength channels are different, and the effective signals carried by the optical carriers of different wavelength channels can be the same or different.
The foregoing describes some of the terms involved in the present application, and the following describes possible application scenarios of the present application.
Fig. 2a shows a schematic diagram of a possible application scenario provided by the present application. The application scenario is exemplified by a forward communication system. The forwarding communication system may include a local device 201, an end device (or called a remote device) 202, and optical fibers for connecting the local device 201 and the end device 202. Different wavelength channels may be transmitted between the local device 201 and the end device 202 via optical fibers, which may also be referred to as trunk fibers (or as feeder fibers or forwarding fibers), typically having lengths greater than 5 km. Illustratively, the direction in which the wavelength channels are transmitted from the local device 201 to the end device 202 may be referred to as a downstream direction, and the direction in which the wavelength channels are transmitted from the end device 202 to the local device 201 may be referred to as an upstream direction.
The local side apparatus 201 includes a baseband unit 2011 and a multiplexer/de-multiplexer (MUX/DMUX) 2012 (or referred to as a wavelength division multiplexer/demultiplexer, or a forward aggregation unit (fronthaul aggregation unit, FAU), or a passive multiplexer/demultiplexer). The baseband unit 2011 refers to a communication device or a functional module having a baseband signal processing function. The baseband unit 2011 may be, for example, a cu+du, a baseband processing unit (building base band unit, BBU), or the like. The MUX/DMUX2012 is based on WDM technology to transmit wavelength channels. Specific: the wavelength channels of at least two different wavelengths from the baseband unit 2011 are converged together by the combiner and coupled into the trunk optical fiber, and transmitted to the end device 202 through the trunk optical fiber; and/or separating the wavelength channels from the at least two different wavelengths in the trunk optical fiber, which are converged together, by a demultiplexer to obtain each independent wavelength channel. Further, the local side apparatus 201 may further include an active device 2013, where the active device 2013 includes, but is not limited to, an optical transport network (optical transport network, OTN), and the OTN is composed of a series of optical network elements connected by optical fiber links, and functions that can be provided may include, but are not limited to, transmission, multiplexing, routing, and short-range and long-range transmission of optical channels.
The end device 202 includes one or more radio frequency units (radio frequency unit, RU) 2021 and MUX/DMUX2022. The rf unit 2021 refers to a communication device or a functional module having an intermediate frequency signal, an rf signal, or an rf signal processing function. The radio frequency unit 2021 may be, for example, an active antenna unit (active antenna unit, AAU) or a remote radio frequency unit (radio remote unit, RRU). One end of the backbone fiber is connected with the MUX/DMUX2012 and the other end of the backbone fiber is connected with the MUX/DMUX2022. The MUX/DMUX2022 is also based on WDM technology to transmit wavelength channels. Specific: the wavelength channels of at least two different wavelengths from the rf unit 2021 are converged together by the combiner and coupled into the trunk optical fiber, and transmitted to the local device 201 through the trunk optical fiber; and/or separating the wavelength channels from the at least two different wavelengths in the trunk optical fiber, which are converged together, by a demultiplexer to obtain each independent wavelength channel. It should be noted that the multiplexer and demultiplexer in the MUX/DMUX2012 and the MUX/DMUX2022 may be integrated together, or may be two independent entities, which is not limited by the present application.
In one possible implementation, the office device 201 may be disposed in a machine room (or referred to as a central office (central office) or Central Office (CO)), and the machine room may further include a server or the like. Wherein the server is used for calculation, information processing and the like. The end device 202 is typically located on the site side.
It will be appreciated that in the foregoing forward communication system, a plurality of end devices 202 and a plurality of MUX/DMUX2012 may be included, and referring to fig. 2b, three end devices 202 and three MUX/DMUX2012 are taken as examples. Further, the forward communication system may also include two fiber optic enclosures, fiber optic enclosure 203 and fiber optic enclosure 204, respectively. The first end of the fiber optic distribution box 203 is connected to one end of three MUX/DMUX2012 in the local device 201 by three trunk fibers, and the second end of the fiber optic distribution box 203 is connected to the first end of the fiber optic distribution box 204 by two trunk fibers and to one end device 202 by one trunk fiber. The second end of the fiber optic distribution box 204 is connected to two end devices 202 by two backbone fibers, respectively.
It should be noted that the above-mentioned scenario is provided for more clearly describing the technical solution of the present application, and does not constitute a limitation of the technical solution provided by the present application, and the optical communication system provided by the present application may be applied to various other possible scenarios, for example, other possible short-range communication systems besides a wireless access communication system (may be simply referred to as a C-RAN system) based on centralized unified processing (centralized processing), cooperative radio (collaborative radio) and real-time closed, such as an ultra-high reliability low latency (ultra-high reliability and low latency, URLLC) communication system, a highly synchronized metropolitan access network system, a multiple-access edge computing (Multi-access Edge Computing, MEC) system, or an interconnection system in a data center.
In one possible implementation, the optical communication system of the present application may support at least one of 50 gigabit per second (Gb/s) 4-level pulse amplitude modulation (PAM-4), non-return-to-zero (NRZ) modulation, or polarization multiplexing coherent modulation, where Gb/s represents the transmission rate.
In one possible implementation, the aforementioned forward communication system may be, for example, a wavelength division multiplexing (LAN WDM) system based on channels in a Local Area Network (LAN), or other possible wavelength division multiplexing systems, which are not listed here.
As an example of an LWDM system, LWDM may employ 12 bands in the range of 1269nm to 1332nm of the O band, and for the center frequency, center wavelength, and wavelength ranges of the 12 bands of the LWDM system, see table 1 below.
TABLE 1 12 band distribution for LWDM System defined by ITU-T G.owdm
In one possible implementation, the 12 wavelength channels may be referred to as the 1 st wavelength Channel (Channel-1, CH 1), the 2 nd wavelength Channel (Channel-2, CH 2), the 3 rd wavelength Channel (Channel-3, CH 3), the 4 th wavelength Channel (Channel-4, CH 4), the 5 th wavelength Channel (Channel-5, CH 5), the 6 th wavelength Channel (Channel-6, CH 6), the 7 th wavelength Channel (Channel-7, CH 7), the 8 th wavelength Channel (Channel-8, CH 8), the 9 th wavelength Channel (Channel-9, CH 9), the 10 th wavelength Channel (Channel-10, CH 10), the 11 th wavelength Channel (Channel-11, CH 11), the 12 th wavelength Channel (Channel-12, CH 12) in order of small wavelengths. In other words, CH1 denotes the 1 st wavelength channel, CH2 denotes the 2 nd wavelength channel, CH3 denotes the 3 rd wavelength channel, CH4 denotes the 4 th wavelength channel, CH5 denotes the 5 th wavelength channel, CH6 denotes the 6 th wavelength channel, CH7 denotes the 7 th wavelength channel, CH8 denotes the 8 th wavelength channel, CH9 denotes the 9 th wavelength channel, CH10 denotes the 10 th wavelength channel, CH11 denotes the 11 th wavelength channel, and CH12 denotes the 12 th wavelength channel.
In conjunction with fig. 2a or fig. 2b, 6 wavelength channels of the 12 wavelength channels are wavelength channels that the local side device 201 transmits to the end device 202, or may be understood that 6 wavelength channels are wavelength channels that the end device 202 receives from the local side device 201 (may be referred to as first direction wavelength channels), and the first direction is a downstream direction; the other 6 wavelength channels are wavelength channels that the end device 202 transmits to the local device 201, or may be understood as wavelength channels that the local device 201 receives from the end device 202 (may be referred to as second direction wavelength channels), and the second direction is an uplink direction.
One possible wavelength channel distribution can be seen in fig. 3, the order of arrival of the wavelengths of the 6 first direction wavelength channels and the 6 second direction wavelength channels is: a first directional wavelength channel (CH 1), a first directional wavelength channel (CH 2), a first directional wavelength channel (CH 3), a first directional wavelength channel (CH 4), a first directional wavelength channel (CH 5), a first directional wavelength channel (CH 6), a second directional wavelength channel (CH 7), a second directional wavelength channel (CH 8), a second directional wavelength channel (CH 9), a second directional wavelength channel (CH 10), a second directional wavelength channel (CH 11), a second directional wavelength channel (CH 12), i.e. the distribution of the first directional wavelength channels may be denoted CH1-CH2-CH3-CH4-CH5-CH6, indicated by the downward arrow; the distribution of wavelength channels in the second direction may be denoted as CH7-CH8-CH9-CH10-CH11-CH12, indicated by the upward arrow. Further, taking 6 first direction wavelength channels and 6 second direction wavelength channels (12 wavelength channels in total) as examples, 6 AAUs (AAU 1-AAU2-AAU3-AAU4-AAU5-AAU6, respectively) may be corresponding, i.e., CH1 input AAU1, CH2 input AAU2, CH3 input AAU3, CH4 input AAU4, CH5 input AAU5, CH6 input AAU6.CH7 from AAU1, CH8 from AAU2, CH9 from AAU3, CH10 from AAU4, CH11 from AAU5, and CH12 from AAU6.
The distribution of 6 first direction wavelength channels and 6 second direction wavelength channels based on the above-described fig. 3 may produce a severe four-wave mixing effect. Specifically, if the ZDW of the optical fiber is between CH9 and CH10 (see fig. 3), CH8, CH9, CH10, CH11 and CH12 are located in the ZDW region of the optical fiber, it can be determined based on the principle of generating four-wave mixing, and the co-transmitted CH8, CH9, CH10 and CH11 may interfere (or be called as damage) with CH9 and CH10, so that the CH8, CH9, CH10 and CH11 may generate a severe four-wave mixing effect, and the four-wave mixing is non-degenerate four-wave mixing. Moreover, CH7, CH9, CH10 and CH12 transmitted in the same direction may also damage CH9 and CH10, i.e., CH7, CH9, CH10 and CH12 may also generate a severe four-wave mixing effect, which is also non-degenerate four-wave mixing. The four wavelength channels of CH8, CH9, CH10 and CH11 are the same in interval, and the four wavelength channels of CH7, CH9, CH10 and CH12 are different in interval. Thus, the spacing of the four wavelength channels that produce the nondegenerate four-wave mixing may be the same or may be different. In other words, the four wavelength channels transmitted in the same direction may have the same or different intervals, which may generate serious four-wave mixing effect.
Referring to fig. 4, another schematic diagram of four-wave mixing is provided in the present application. If the ZDW of the optical fiber is located in CH9, or understood that the ZDW of the optical fiber coincides with CH9, and CH8, CH9, CH10, CH11, and CH12 are located in the ZDW region to which the ZDW of the optical fiber belongs, it can be determined that the co-propagating CH8, CH9, and CH10 produce a severe four-wave mixing effect, which is degenerate four-wave mixing, based on the description of the principle of four-wave mixing described above. Moreover, co-transmitted CH7, CH9 and CH11 produce a degenerate four-wave mixing effect.
It should be noted that four-wave mixing may also occur on the four wavelength channels of the interactions outside the ZDW region, and in conjunction with fig. 3 or 4 described above, for example, CH1, CH2, CH3, and CH4, or CH2, CH3, CH4, and CH5, or CH3, CH4, CH5, and CH6, or CH1, CH3, CH4, and CH6, etc., all produce non-degenerate four-wave mixing. Furthermore, one wavelength channel may be affected by multiple sets of four-wave mixing effects. For example, CH3 may be affected by mixing effects from four groups CH1-CH2-CH3-CH4, CH2-CH3-CH4-CH5, CH3-CH4-CH5-CH6, and CH1-CH3-CH4-CH 6.
In view of the above, the present application proposes an optical communication system. The optical communication system can reduce or inhibit the four-wave mixing effect, thereby improving the performance of the optical communication system.
Based on the foregoing, the optical communication system according to the present application will be specifically described with reference to fig. 5, fig. 6a to fig. 6b, fig. 7a to fig. 7b, fig. 8a to fig. 8b, fig. 9a to fig. 9b, and fig. 10 to fig. 12.
Fig. 5 is a schematic diagram of an optical communication system according to the present application. The optical communication system may include a first node, a second node, and an optical fiber for connecting the first node and the second node. The first node may be the local device 201 in fig. 2a or fig. 2b, and the second node may be the terminal device 202 in fig. 2a or fig. 2 b. It should be noted that the first node may include more or less structures than the local side device 201, and the second node may include more or less structures than the terminal device 202, which is not limited by the present application. Alternatively, the first node may be the end device 202 in fig. 2a or fig. 2b, and the second node may be the local device 201 in fig. 2a or fig. 2 b. It will be appreciated that the first node may include more or fewer structures than the end device 202, and the second node may include more or fewer structures than the local device 201, which is not limited by the present application. The wavelength channel transmitted by the first node to the second node may be referred to as a first direction wavelength channel, and the wavelength channel transmitted by the second node to the first node may be referred to as a second direction wavelength channel. In other words, the N first direction wavelength channels are wavelength channels transmitting in the same direction, and the N second direction wavelength channels are wavelength channels transmitting in the same direction.
The optical fiber used to connect the first node and the second node may be referred to as a backbone fiber, the ZDW of which belongs to one ZDW region. The optical fiber may be, for example, a standard single-mode fiber (SSMF), and the ZDW of the standard single-mode fiber may have a ZDW region in the range of [1300nm,1324nm ]. It is also understood that the ZDWs of different optical fibers may be different, the ZDWs of different standard single mode fibers being one of the ZDW regions to which they belong. The optical fiber is used for transmitting N first-direction wavelength channels and N second-direction wavelength channels, wherein N is an integer greater than 2. Wherein the at least two first direction wavelength channels and the at least one second direction wavelength channel are located in the ZDW region, or the at least two second direction wavelength channels and the at least one first direction wavelength channel are located in the ZDW region. The mixed distribution of first-direction wavelength channels and second-direction wavelength channels in the ZDW region can also be understood as: in the ZDW region, the number of consecutively adjacent first-direction wavelength-channels is less than or equal to 2, and the number of consecutively adjacent second-direction wavelength-channels is less than or equal to 2. Further, in some possible embodiments, at least two first direction wavelength channels and at least two second direction wavelength channels are located in the ZDW region, and the first direction wavelength channels and the second direction wavelength channels located in the ZDW region are mixed and distributed.
Based on the optical communication system, through mixed distribution of the first-direction wavelength channels and the second-direction wavelength channels in the ZDW area, on one hand, the interval between the wavelength channels in the same direction transmission is increased; on the other hand, the method helps to reduce the number of four-wave mixing or can eliminate four-wave mixing, for example, the four-wave mixing can be formed by 3 groups of first-direction wavelength channels based on the prior art distribution mode, but the four-wave mixing can be formed by at most 2 groups of first-direction wavelength channels based on the optical communication system. Based on this, it is useful to reduce or suppress the four-wave mixing effect, so that deterioration in performance of the optical communication system due to four-wave mixing can be suppressed. Further, since the same optical fiber is used for the transmission of the first-direction wavelength channel and the transmission of the second-direction wavelength channel, the first node and the second node have better synchronization quality.
The following description describes the respective structures shown in fig. 5 to give an exemplary implementation.
1. Optical fiber
In one possible implementation, an optical fiber is used to transmit N first-direction wavelength channels and N second-direction wavelength channels. The intensity of the four-wave mixing effect in the fiber is related to the ZDW (or ZDF) of the fiber, the distribution of the N first-direction wavelength channels and the N second-direction wavelength channels, etc.
The following exemplary conditions that are satisfied by the distribution of the N first direction wavelength channels and the N second direction wavelength channels are given to achieve attenuation or suppression of the four-wave mixing effect of the optical fiber.
In condition 1, among the wavelength channels (first-direction wavelength channels or second-direction wavelength channels) propagating in the same direction, the center (or referred to as symmetry axis or center) of the wavelength channels where there are no four symmetries is located in the ZDW region.
The four symmetrical wavelength channels mean that the wavelengths (or frequencies) of the four wavelength channels are symmetrical about the wavelength center (or frequency center) of the four wavelength channels. With reference to FIG. 1a, the four wavelength channels have a frequency center v 1 And v 2 Center (i.e. v) 0 ＝v 1 + v 2 /2)，v 1 、v 2 、v 3 And v 4 As about the frequency centre v 0 Four symmetrical wavelength channels are symmetrical. In connection with the above-described fig. 3, taking CH8, CH9, CH10, and CH11 as examples, the wavelength centers λ0 of CH8, CH9, CH10, and CH11 coincide with ZDW, and CH8, CH9, CH10, and CH11 are four symmetrical wavelength channels symmetrical about the wavelength center λ0, and in order to reduce or suppress the four-wave mixing effect of the optical fiber, there is no distribution of CH8, CH9, CH10, and CH11 in the wavelength channels transmitted in the same direction.
Specifically, among the N first-direction wavelength channels, there are no four symmetrical first-direction wavelength channels, the center of which is located in the ZDW region; and/or, among the N second-direction wavelength channels, there are also no four symmetrical second-direction wavelength channels whose centers are located in the ZDW region.
Since severe four-wave mixing occurs in the ZDW region of the optical fiber, if the distribution of the N first-direction wavelength channels and the N second-direction wavelength channels satisfies the above condition 1, four-wave mixing does not occur in the ZDW region, and therefore, the distribution of the N first-direction wavelength channels and the N second-direction wavelength channels satisfying the above condition 1 can reduce or suppress the non-degenerate four-wave mixing effect.
Further, the four-wave mixing further includes a degenerate four-wave mixing effect, and if the distribution of the N first-direction wavelength channels and the N second-direction wavelength channels satisfies the following condition 2, attenuation or suppression of the degenerate four-wave mixing effect can be achieved.
In condition 2, among the wavelength channels propagating in the same direction, there are no three wavelength channels which are equally spaced and at least two of which are located in the ZDW region.
In one possible implementation, the spacing between wavelength channels may be characterized by frequency spacing, or may also be characterized by wavelength spacing. In connection with fig. 4, taking CH8, CH9 and CH10 as examples, the wavelength intervals of the three wavelength channels are the same, and CH8, CH9 and CH10 are all located in the ZDW region, so that in order to weaken or suppress four-wave mixing of the optical fiber, in the wavelength channels transmitted in the same direction, there is no distribution of CH8, CH9 and CH 10.
Specifically, among the N first-direction wavelength channels, there are no three first-direction wavelength channels which have the same interval and at least two of which are located in the ZDW region; and/or, there are no three second direction wavelength channels with the same interval and at least two of which are located in the ZDW region, among the N second direction wavelength channels. It is also understood that there are no N first-direction wavelength channels: three equally spaced first-direction wavelength channels and two of the three equally spaced first-direction wavelength channels are located in the ZDW region; and/or, among the N second-direction wavelength channels, there are no: three equally spaced second-direction wavelength channels and two of the three equally spaced second-direction wavelength channels are located in the ZDW region.
It can be appreciated that if the distribution of the N wavelength channels in the first direction only satisfies the above condition 1, the nondegenerate four-wave mixing effect in the first direction can be reduced or suppressed; if the distribution of the N first-direction wavelength channels satisfies only the above condition 2, the degenerate four-wave mixing effect in the first direction can be reduced or suppressed, and if the distribution of the N first-direction wavelength channels satisfies both the above condition 1 and the above condition 2, the non-degenerate four-wave mixing effect in the first direction can be reduced or suppressed, and the degenerate four-wave mixing effect in the first direction can be reduced or suppressed. Similarly, the distribution of the N second-direction wavelength channels may also attenuate or suppress the non-degenerate four-wave mixing effect and/or the degenerate four-wave mixing effect, which are not described herein.
In one possible implementation, attenuation of the four-wave mixing effect in the fiber may also be achieved by increasing the spacing of adjacent wavelength channels, particularly in the ZDW region.
By simulation it can be determined that: the polarization states of the wavelength channels that interact during transmission of the fiber may change differently due to polarization-mode dispersion (PMD). The four-wave mixing effect is strongest when the polarization states of the wavelength channels generating the four-wave mixing are the same, so that the four-wave mixing effect is weakened when the polarization states of the wavelength channels in interaction are different. For example, the fiber has a polarization mode dispersion coefficient of 0.1 picoseconds/square root kilometersThe wavelength channel is transmitted over a 5km fiber with an average differential group delay (differential group delay, DGD) of about 0.22ps due to polarization mode dispersion. This illustrates that during a 5km transmission, two wavelength channels separated by approximately 4.5THz change 360 degrees relative to the average polarization. It is also understood that when the interval between two wavelength channels transmitted in the same direction is 4.5THz, the polarization state changes by 360 degrees on average, so that the four-wave mixing effect can be reduced or suppressed.
Based on this, when the interval of the two wavelength channels with the largest interval among the wavelength channels propagating in the same direction is greater than or equal to 4.5THz, the above-mentioned condition 1 and condition 2 can be appropriately relaxed. For example, condition 1 may be relaxed to condition 3 below, and condition 2 may be relaxed to condition 4 below. Referring to fig. 3, CH8, CH9, CH10, CH11, and CH12 are located in the ZDW region to which the ZDW of the optical fiber belongs, and when the interval between CH8 and CH12 is 4.5THz or more, the condition 1 may be relaxed to the following condition 3, the condition 2 may be relaxed to the following condition 4, and also the attenuation or suppression of four-wave mixing in the optical fiber may be achieved.
And 3, the interval of two wavelength channels with the largest interval in the wavelength channels which are co-propagating in the ZDW area is larger than or equal to a threshold value, and the centers of four symmetrical wavelength channels which are allowed to exist in the wavelength channels which are co-propagating at most are positioned in the ZDW area.
Wherein the threshold value may be equal to or greater than 4.5THz, for example.
Specifically, among the N first-direction wavelength channels, the center of the first-direction wavelength channel, where at most four symmetry directions are allowed to exist, is located in the ZDW region; and/or, in the N second direction wavelength channels, at most, the centers of the four second direction wavelength channels are allowed to be located symmetrically in the ZDW region.
Condition 4, the interval between the two wavelength channels with the largest interval among the wavelength channels propagating in the same direction in the ZDW region is greater than or equal to the threshold, and the maximum allowable existence among the wavelength channels propagating in the same direction is: three wavelength channels equally spaced and at least two of which are located in the ZDW region.
Specifically, among the N first-direction wavelength channels, at most the allowed exists: three first-direction wavelength channels equally spaced and at least two of which are located in the ZDW region; and/or, at most, the N second-direction wavelength channels are allowed to exist: three second direction wavelength channels equally spaced and at least two of which are located in the ZDW region. It is also understood that, out of the N first-direction wavelength channels, at most three first-direction wavelength channels are allowed to satisfy: at least two of the three first-direction wavelength channels that are equally spaced and equally spaced are located in the ZDW region; and/or, in the N second direction wavelength channels, at most three second direction wavelength channels are allowed to satisfy: at least two of the three second-direction wavelength channels that are equally spaced and equally spaced are located in the ZDW region.
To ensure that the optical fiber transmits the wavelength channels normally, the spacing of the individual wavelength channels needs to be controlled. If the spacing is too small, interference between wavelength channels is liable to occur. If the spacing is too large, the utilization of the fiber is reduced. In a possible implementation, the minimum frequency separation of the N first direction wavelength channels and the N second direction wavelength channels of the hybrid distribution is equal to 800GHz. It is also understood that among the 2N wavelength channels (including N first-direction wavelength channels and N second-direction wavelength channels), the minimum frequency interval between adjacent two wavelength channels is equal to 800GHz. In another possible implementation, the minimum frequency separation of the N first direction wavelength channels and the N second direction wavelength channels of the hybrid distribution is equal to 400GHz. It is also understood that among the 2N wavelength channels (including N first-direction wavelength channels and N second-direction wavelength channels), the minimum frequency interval between adjacent two wavelength channels is equal to 400GHz. The adjacent two wavelength channels may be a first direction wavelength channel and a first direction wavelength channel, or may also be a second direction wavelength channel and a second direction wavelength channel, or may also be a first direction wavelength channel and a second direction wavelength channel. By setting the minimum frequency interval to 400GHz, the band resource can be fully utilized, the transmission capacity of the optical fiber can be improved, and the utilization efficiency of the optical fiber resource can be improved.
In one possible implementation, N may be 6, i.e., the optical communication system may employ 12 wavelength channels for transmission, and the spacing between adjacent wavelength channels after mixing may be 400GHz or 800GHz. Alternatively, N may be equal to 12, that is, the optical communication system may use 24 wavelength channels for transmission, and the interval between adjacent wavelength channels after mixing may be 400GHz or 800GHz, so that the aggregation capacity of the optical fiber may be further increased. It should be noted that N may have other values, and the specific value of N is not limited in the present application.
To facilitate further understanding of the scheme, n=6, i.e. 6 first direction wavelength channels and 6 second direction wavelength channels, are described as examples below. A total of 12 wavelength channels, and the distribution scheme of these 12 wavelength channels with 2ζ6=64 possible wavelength channels is shown in table 2. A in table 2 indicates that in an adjacent pair of wavelength channels (adjacent first-direction wavelength channels and second-direction wavelength channels corresponding to the same first optical transceiver may be referred to as a pair of wavelength channels, and adjacent first-direction wavelength channels and second-direction wavelength channels corresponding to the same second optical transceiver may be referred to as a pair of wavelength channels, and the wavelength of the first-direction wavelength channels is shorter than the wavelength of the second-direction wavelength channels, see the related description below for details). B represents that the wavelength of the first direction wavelength channel is longer than the wavelength of the second direction wavelength channel in the adjacent pair of wavelength channels. In other words, wavelengths are distributed in order of arrival from small, and the wavelength channel distribution denoted by a is: a first direction wavelength channel, a second direction wavelength channel. The wavelength channel distribution represented by B is: a second direction wavelength channel, a first direction wavelength channel. 1 denotes a first direction wavelength channel and 0 denotes a second direction wavelength channel.
Table 2 6 distribution of first-direction wavelength channels and 6 second-direction wavelength channels
It should be noted that any of the above-described mixed distributions of 64 12 wavelength channels given in table 2 may reduce or suppress four-wave mixing as compared to the distribution of fig. 3 or 4. In order to further attenuate or suppress the four-wave mixing of the optical fiber, the N first-direction wavelength channels and the N second-direction wavelength channels also need to satisfy the above-described condition 3 and/or condition 4, and in order to still further attenuate or suppress the four-wave mixing of the optical fiber, the N first-direction wavelength channels and the N second-direction wavelength channels also need to satisfy the above-described condition 1 and/or condition 2.
In the following, taking n=6 as an example in combination with the above table 2, 4 schemes of 6 first direction wavelength channels and 6 second direction wavelength channels are exemplarily given, and the distribution of 6 first direction wavelength channels and 6 second direction wavelength channels in the 4 schemes can meet the above condition 1 and condition 2, which can effectively reduce or suppress the four-wave mixing effect.
In the following description, the first-direction wavelength channel and the second-direction wavelength channel in each rectangular frame in fig. 6a, 6b, 7a, 7b, 8a, 8b, 9a, and 9b may be referred to as one wavelength channel pair.
Scheme 1,6 first direction wavelength channels alternate (or are referred to as cross-distribution) with 6 second direction wavelength channels.
It is also understood that the second direction wavelength channel is adjacent to the first direction wavelength channel and the first direction wavelength channel is adjacent to the second direction wavelength channel.
In one possible implementation, the spacing Δ of the 6 first-direction wavelength channels 11 The same and the wavelength intervals delta of 6 second direction wavelength channels 21 The same applies. Further, the wavelength interval delta of the first direction wavelength channel 11 The same wavelength interval as the wavelength channels of the second direction can be seen in fig. 6a described below.
The wavelength of the first direction wavelength channel is longer or shorter than the wavelength of the second direction wavelength channel in the pair of wavelength channels, and the following two schemes can be adopted.
In the embodiment 1.1, the wavelength of the first direction wavelength channel is shorter than the wavelength of the second direction wavelength channel in the wavelength channel pair.
Fig. 6a is a schematic diagram showing a distribution of wavelength channels according to the present application. The distribution diagram of the wavelength channels corresponds to the number 1 in table 2. Adjacent CH1 and CH2 are a wavelength channel pair, adjacent CH3 and CH4 are a wavelength channel pair, adjacent CH5 and CH6 are a wavelength channel pair, adjacent CH7 and CH8 are a wavelength channel pair, adjacent CH9 and CH10 are a wavelength channel pair, and adjacent CH11 and CH12 are a wavelength channel pair. The 6 first direction wavelength channels and the 6 second direction wavelength channels are distributed in order from small to large: the first direction wavelength channel, the second direction wavelength channel, the first direction wavelength channel, the second direction wavelength channel. Alternatively, the 6 first direction wavelength channels may be distributed over the 1 st, 3 rd, 5 th, 7 th, 9 th and 11 th wavelength channels, and may be expressed as: CH1-CH3-CH5-CH7-CH9-CH11; the 6 second-direction wavelength channels are distributed over the 2 nd, 4 th, 6 th, 8 th, 10 th and 12 th wavelength channels, and can be expressed as: CH2-CH4-CH6-CH8-CH10-CH12.
With scheme 1.1 above, there is a set of first wavelength channel distributions (i.e., CH6-CH8-CH10-CH 12) that may cause more severe nondegenerate four-wave mixing. However, since the interval between the N first direction wavelength channels is doubled compared to fig. 3, and since the four-wave mixing effect can be reduced by increasing the interval between the wavelength channels, the four-wave mixing effect of the N first direction wavelength channels on the optical fiber can be reduced based on the distribution of the above-mentioned scheme 1.1. Similarly, the four-wave mixing effect (or called four-wave mixing damage) of the N second-direction wavelength channels on the optical fiber can be reduced.
In the embodiment 1.2, the wavelength of the first direction wavelength channel is longer than the wavelength of the second direction wavelength channel in the pair of wavelength channels.
Fig. 6b is a schematic diagram showing another wavelength channel distribution according to the present application. The distribution diagram of the wavelength channels corresponds to the number 33 in table 2. The description of the wavelength channel pair may be referred to the description in the foregoing scheme 1.1, and will not be repeated here. The 6 first direction wavelength channels and the 6 second direction wavelength channels are distributed in order from small to large: the second direction wavelength channel, the first direction wavelength channel, the second direction wavelength channel, the first direction wavelength channel. Can also be expressed as: distribution mode of 6 first-direction wavelength channels: the CH2-CH4-CH6-CH8-CH10-CH12, i.e., the 6 first direction wavelength channels are distributed over the 2 nd, 4 th, 6 th, 8 th, 10 th and 12 th wavelength channels. Distribution mode of 6 wavelength channels in the second direction: the CH1-CH3-CH5-CH7-CH9-CH11, i.e., the 6 second-direction wavelength channels are distributed over the 1 st, 3 rd, 5 th, 7 th, 9 th and 11 th wavelength channels.
Through the above scheme 1.2, the four-wave mixing effect of the N first direction wavelength channels and the N second direction wavelength channels on the optical fiber can also be reduced, and the detailed analysis can be referred to the description of the foregoing scheme 1.1, which is not repeated here.
In one possible implementation, the spacing Δ between adjacent wavelength channels (i.e., first-direction wavelength channels and second-direction wavelength channels) of the mixed distribution is equal to 800GHz. In connection with the above-described fig. 6a or 6b, the spacing delta between CH1 and CH2 is equal to 800GHz, and the spacing delta between CH2 and CH3 is also equal to 800GHz. Alternatively, the spacing Δ between adjacent two wavelength channels of the mixed distribution (i.e., the first direction wavelength channel and the second direction wavelength channel) is equal to 400GHz. In connection with the above-mentioned fig. 6a, the spacing delta between CH1 and CH2 is equal to 400GHz, and the spacing delta between CH2 and CH3 is also equal to 400GHz.
Further, the spacing Δ of adjacent first-direction wavelength channels in FIG. 6a or FIG. 6b 11 Equal to 2 times the spacing delta between adjacent wavelength channels of the mixed distribution, the spacing delta between adjacent wavelength channels in the second direction 21 Equal to 2 times the spacing delta between adjacent wavelength channels of the mixed distribution.
Scheme 2, the intervals of 6 wavelength channels propagating in the same direction are different, specifically, the first direction and the second direction in one of the wavelength channel pairs in fig. 6a or fig. 6b are interchanged (or referred to as flipping).
Specifically, the 6 first-direction wavelength channels are different in interval, and the 6 second-direction wavelength channels are different in interval. Further, among the 6 first-direction wavelength channels, the intervals of the first-direction wavelength channels located in the ZDW region are different, and among the 6 second-direction wavelength channels, the intervals of the second-direction wavelength channels located in the ZDW region are different.
The wavelength of the first direction wavelength channel based on the first wavelength channel pair is longer or shorter than the wavelength of the second direction wavelength channel, and the following two schemes can be further adopted.
Scheme 2.1, the wavelength of the first direction wavelength channel is shorter than the wavelength of the second direction wavelength channel.
Fig. 7a is a schematic diagram showing a distribution of wavelength channels according to another embodiment of the present application. The distribution diagram of the wavelength channels corresponds to the number 5 in table 2. The description of the wavelength channel pair may be referred to the description in the foregoing scheme 1.1, and will not be repeated here. The 6 first direction wavelength channels and the 6 second direction wavelength channels are distributed in order from small to large: a first direction wavelength channel, a second direction wavelength channel, a first direction wavelength channel a second direction wavelength channel, a first direction wavelength channel, a second direction wavelength channel the second direction wavelength channel, the first direction wavelength channel, the second direction wavelength channel. Or may be expressed as a distribution manner of the 6 first direction wavelength channels: the distribution mode of the CH1-CH3-CH5-CH8-CH9-CH11 and 6 wavelength channels in the second direction is as follows: CH2-CH4-CH6-CH7-CH10-CH12. It will be appreciated that fig. 7a corresponds to the sequential exchange of the first and second directions of CH7 and CH8 of fig. 6 a. Specifically, the 7 th wavelength channel in fig. 6a is a first direction wavelength channel, and the 7 th wavelength channel in fig. 7a is a second direction wavelength channel. The 8 th wavelength channel in fig. 6a is the second direction wavelength channel, and the 8 th wavelength channel in fig. 7a is the first direction wavelength channel.
Further, the wavelength intervals of the 6 first-direction wavelength channels are different, and the wavelength intervals of the 6 second-direction wavelength channels are also different. Referring to fig. 7a, the wavelength intervals of the 6 first direction wavelength channels have three sizes, namely, the wavelength interval delta 11 、Δ 12 、Δ 13 The wavelength intervals of the 6 second-direction wavelength channels also include three magnitudes, respectively Δ 21 、Δ 22 、Δ 23 . Further, among the 6 first-direction wavelength channels, the intervals of the first-direction wavelength channels located in the ZDW region are different, and among the 6 second-direction wavelength channels, the intervals of the second-direction wavelength channels located in the ZDW region are different.
In combination with table 1, taking the ZDW region to which the standard single mode fiber belongs as an example, the ZDW regions are in CH8, CH9, CH10, CH11 and CH12, so that the four-wave mixing can be further weakened by reversing the directions of CH7 and CH 8.
In general, the 5 wavelength channels of the 12 wavelength channels with the longest wavelength (CH 8, CH9, CH10, CH11 and CH12 are located in the ZDW region, respectively) are distributed in order of the wavelengths from small to large, so that interchanging the first and second directions of the wavelength channels located in the ZDW region helps to further attenuate or suppress four-wave mixing, further, CH8, CH9 and CH11 are located in the ZDW region, these three first-direction wavelength channels do not produce four-wave mixing, and 6 first-direction wavelength channels satisfy that there are no four symmetrical first-direction wavelength channels with centers located in the ZDW region, and 6 first-direction wavelength channels do not exist, three first-direction wavelength channels with the same interval and at least two of them located in the ZDW region are CH10 and CH12, these two second-direction wavelength channels also do not produce four-wave mixing, and 6 second-direction wavelength channels also satisfy that there are no four symmetrical first-direction wavelength channels with the same interval and at least two of them located in the ZDW region are located in the first-direction wavelength channels with the second-direction channel, and the second-direction channels are located in the second-direction channel is at least 1, and the second-direction channels are located in the second-direction channel is at least on the basis of the same interval, and the two-direction channel is suppressed in the second-direction channel is located in the second-direction 1, or the second-channel is further on the condition 1.
It should be noted that, in the 12 wavelength channels distribution of the above-mentioned scheme 2.1, four symmetrical first-direction wavelength channels, that is, CH1, CH3, CH9, and CH11 (where CH9 and CH11 are in the ZDW region) still exist in the 6 first-direction wavelength channels, but the centers of the four symmetrical first-direction wavelength channels are located between CH6 and CH7, so that the four-wave mixing effect is weak. Similarly, four symmetrical second-direction wavelength channels, namely CH2, CH4, CH10 and CH12, exist in the 6 second-direction wavelength channels, and the centers of the four symmetrical second-direction wavelength channels are located between CH6 and CH7, so that the four-wave mixing effect is weak.
Scheme 2.2, the wavelength of the first direction wavelength channel is longer than the wavelength of the second direction wavelength channel.
Fig. 7b is a schematic diagram showing a distribution of wavelength channels according to another embodiment of the present application. The distribution diagram of the wavelength channels corresponds to the sequence number 37 in table 2. The description of the wavelength channel pair may be referred to the description in the foregoing scheme 1.1, and will not be repeated here. The 6 first direction wavelength channels and the 6 second direction wavelength channels are distributed in order from small to large: a second direction wavelength channel, a first direction wavelength channel, a second direction wavelength channel, a first direction wavelength channel the first direction wavelength channel, the second direction wavelength channel, the first direction wavelength channel. Or may be expressed as a distribution of 6 first-direction wavelength channels: distribution mode of CH2-CH4-CH6-CH7-CH10-CH12,6 wavelength channels in the second direction: CH1-CH3-CH5-CH8-CH9-CH11. It will be appreciated that fig. 7b corresponds to the first and second direction inversions of CH7 and CH8 of fig. 6 b. Specifically, the 7 th wavelength channel in fig. 6b is the second direction wavelength channel, and the 7 th wavelength channel in fig. 7b is the first direction wavelength channel. The 8 th wavelength channel in fig. 6b is the first direction wavelength channel, and the 8 th wavelength channel in fig. 7b is the second direction wavelength channel.
The four-wave mixing effect of the optical fiber can be reduced or suppressed based on the distribution of the 6 first-direction wavelength channels and the 6 second-direction wavelength channels in the above-mentioned scheme 2.2, and the specific analysis can be described in the scheme 2.1, which is not repeated here.
It should be noted that, in the 12 wavelength channel distribution of the above-mentioned scheme 2.2, four symmetrical second-direction wavelength channels, that is, CH1, CH3, CH9, and CH11, exist in the 6 second-direction wavelength channels, but the centers of the four symmetrical second-direction wavelength channels are located between CH6 and CH7, and the interval is large, so that the four-wave mixing effect is weak. Similarly, four symmetrical first-direction wavelength channels, namely CH2, CH4, CH10 and CH12, exist in the 6 first-direction wavelength channels, the centers of the four symmetrical first-direction wavelength channels are positioned between CH6 and CH7, the interval is larger, and the four-wave mixing effect is weaker.
With scheme 2 described above, transmission in the fiber over both the 6 first-direction wavelength channels and the 6 second-direction wavelength channels does not result in severe non-degenerate four-wave mixing (i.e., non-degenerate four-wave mixing). Theoretical simulations have found that based on the distribution of scheme 2 above, the performance degradation caused by four-wave mixing can be reduced by a factor of about 20 compared to the distribution (configuration) of fig. 3. Further, under the condition that the four-wave mixing is inhibited by 20 times, after the LWDM system of the 12-channel 25Gb/s based on NRZ modulation is transmitted by a 10km optical fiber, the four-wave mixing of less than 0.5 decibel (dB) can be achieved; after the transmission of the 12-channel 50Gb/s LWDM system based on PAM-4 modulation through the 10km optical fiber, the performance degradation is less than 2dB, so that the aggregation capacity of the optical fiber can be increased from 300 Gb/s to 600Gb/s. LWDM systems may also employ polarization multiplexing coherent modulation, whereby single wavelength channel rates of 100Gb/s or higher may be achieved.
Scheme 3, the spacing of the 6 wavelength channels propagating in the same direction is different, specifically, the first direction and the second direction in the two wavelength channel pairs based on the above fig. 6a or fig. 6b are reversed (or referred to as interchanged).
Based on this, the wavelength intervals of the 6 first-direction wavelength channels are different, and the wavelength intervals of the 6 second-direction wavelength channels are different. Further, among the 6 first-direction wavelength channels, the intervals of the first-direction wavelength channels located in the ZDW region are different, and among the 6 second-direction wavelength channels, the intervals of the second-direction wavelength channels located in the ZDW region are different.
The wavelength of the first direction wavelength channel based on the first wavelength channel pair is longer or shorter than the wavelength of the second direction wavelength channel, and the following two schemes can be further adopted.
Scheme 3.1, the wavelength of the first direction wavelength channel is shorter than the wavelength of the second direction wavelength channel.
Fig. 8a is a schematic diagram showing a distribution of wavelength channels according to another embodiment of the present application. The distribution diagram of the wavelength channels corresponds to the number 19 in table 2. The 6 first direction wavelength channels and the 6 second direction wavelength channels are distributed in order from small to large: the first direction wavelength channel, the second direction wavelength channel, the first direction wavelength channel, the second direction wavelength channel, the first direction wavelength channel, the second direction wavelength channel. It can also be expressed as a distribution manner of 6 first-direction wavelength channels: distribution mode of CH1-CH4-CH5-CH7-CH10-CH11,6 wavelength channels in the second direction: CH2-CH3-CH6-CH8-CH9-CH12. The description of the wavelength channel pair may be referred to the description in the foregoing scheme 1.1, and will not be repeated here. It will be appreciated that fig. 8a above corresponds to interchanging the first and second directions of CH3 and CH4 of fig. 6a above, and interchanging the first and second directions of CH9 and CH10 above.
Taking the example that CH8, CH9, CH10, CH11 and CH12 are located in the ZDW region, the second-direction wavelength channels are distributed in the 8 th, 9 th and 12 th wavelength channels, and the three second-direction wavelength channels do not generate four-wave mixing; the first direction wavelength channels are distributed between the 10 th and 11 th wavelength channels, and the two first direction wavelength channels do not generate four-wave mixing. Moreover, the 6 first-direction wavelength channels satisfy: there are no four symmetric first direction wavelength channels centered in the ZDW region, nor are there: three first direction wavelength channels, equally spaced and at least two of which are located in the ZDW region. The 6 second direction wavelength channels satisfy: the center of the second direction wavelength channels where there are no four symmetries is located in the ZDW region, nor is there any: three second direction wavelength channels equally spaced and at least two of which are located in the ZDW region. It is also understood that the distribution of 6 first-direction wavelength channels and 6 second-direction wavelength channels based on the above-described scheme 3.1 satisfies the above-described condition 1 and condition 2. Thus, the distribution based on scheme 3.1 above helps to further attenuate or suppress the four-wave mixing effect.
It should be noted that, in the 12 wavelength channels distribution of the above-mentioned scheme 3.1, four symmetrical first-direction wavelength channels exist in the 6 first-direction wavelength channels, that is, CH1, CH4, CH7, and CH10, and the centers of the four symmetrical first-direction wavelength channels are located between CH5 and CH6, so that the four-wave mixing effect is weak. Further, there are four symmetrical first-direction wavelength channels, i.e., CH4, CH5, CH10, CH11, among the 6 first-direction wavelength channels, and the centers of the four symmetrical first-direction wavelength channels are located between CH7 and CH8, so that the four-wave mixing effect caused is weak. Similarly, four symmetrical second-direction wavelength channels, namely CH2, CH3, CH8 and CH9, exist in the N second-direction wavelength channels, and the centers of the four symmetrical second-direction wavelength channels are located between CH5 and CH6, so that the four-wave mixing effect is weak. Further, there are four symmetrical second-direction wavelength channels, i.e., CH3, CH6, CH9, CH12, among the N second-direction wavelength channels, and the centers of the four symmetrical second-direction wavelength channels are located between CH7 and CH8, and thus, the four-wave mixing effect caused is weak.
Scheme 3.2, the wavelength of the first direction wavelength channel is shorter than the wavelength of the second direction wavelength channel.
Fig. 8b is a schematic diagram showing a distribution of wavelength channels according to another embodiment of the present application. The distribution diagram of the wavelength channels corresponds to the sequence number 51 in table 2. The 6 first direction wavelength channels and the 6 second direction wavelength channels are distributed in order from small to large: the second direction wavelength channel, the first direction wavelength channel, the second direction wavelength channel, the first direction wavelength channel. Or may be expressed as a distribution of 6 first-direction wavelength channels: distribution mode of CH2-CH3-CH6-CH8-CH9-CH12,6 wavelength channels in the second direction: CH1-CH4-CH5-CH7-CH10-CH11. It will be appreciated that fig. 8b above corresponds to the first and second directions of CH3 and CH4 in fig. 6b being reversed, and the first and second directions of CH9 and CH10 being reversed.
The four-wave mixing effect of the optical fiber can be reduced or suppressed based on the distribution of the 6 first direction wavelength channels and the 6 second direction wavelength channels in the above scheme 3.2, and the specific analysis can be described in the scheme 3.1, which is not repeated here.
It should be noted that, in the 12 wavelength channel distribution of the above-mentioned scheme 3.2, four symmetrical second-direction wavelength channels, that is, CH1, CH4, CH7, and CH10, exist in the 6 second-direction wavelength channels, and the centers of the four symmetrical second-direction wavelength channels are located between CH5 and CH6, and the interval is large, so that the four-wave mixing effect is weak. Further, there are four symmetrical second-direction wavelength channels, i.e., CH4, CH5, CH10, CH11, among the 6 second-direction wavelength channels, and the centers of the four symmetrical second-direction wavelength channels are located between CH7 and CH8 with a larger interval, so that the four-wave mixing effect is weak. Similarly, four symmetrical first-direction wavelength channels, namely CH2, CH3, CH8 and CH9, exist in the N first-direction wavelength channels, and the centers of the four symmetrical first-direction wavelength channels are positioned between CH5 and CH6, and the interval is larger, so that the four-wave mixing effect is weaker. Further, there are four symmetrical first-direction wavelength channels, i.e., CH3, CH6, CH9, CH12, among the N first-direction wavelength channels, and the centers of the four symmetrical first-direction wavelength channels are located between CH7 and CH8 with a larger interval, so that the four-wave mixing effect is weak.
Transmission in the optical fiber through the above-described schemes 3,6 first-direction wavelength channels and 6 second-direction wavelength channels does not result in severe non-degenerate four-wave mixing (i.e., non-degenerate four-wave mixing). Theoretical simulations have found that based on the profile of this scheme 3, the performance degradation caused by four-wave mixing can be reduced by a factor of about 20 compared to the profile (configuration) of fig. 3. Further analysis of the effects can be found in the description of scheme 2 above, and will not be described in detail here.
Scheme 4, the intervals of 6 wavelength channels propagating in the same direction are different, specifically, based on fig. 6a or fig. 6b, the first direction and the second direction in the three wavelength channel pairs are reversed.
The wavelength of the first direction wavelength channel based on the first wavelength channel pair is longer or shorter than the wavelength of the second direction wavelength channel, and the following two schemes can be further adopted.
Scheme 4.1, the wavelength of the first direction wavelength channel is shorter than the wavelength of the second direction wavelength channel.
Fig. 9a is a schematic diagram showing a distribution of wavelength channels according to another embodiment of the present application. The distribution diagram of the wavelength channels corresponds to the number 28 in table 2. The 6 first direction wavelength channels and the 6 second direction wavelength channels are distributed in order from small to large: the first direction wavelength channel, the second direction wavelength channel, the first direction wavelength channel. Or may be expressed as a distribution of 6 first-direction wavelength channels: distribution mode of CH1-CH4-CH6-CH7-CH10-CH12, 6 wavelength channels in the second direction: CH2-CH3-CH5-CH8-CH9-CH11. The description of the wavelength channel pair may be referred to the description in the foregoing scheme 1.1, and will not be repeated here. It will be appreciated that fig. 9a described above corresponds to the first and second directions of CH3 and CH4, the first and second directions of CH5 and CH6, the first and second directions of CH9 and CH10, and the first and second directions of CH11 and CH12 described above with reference to fig. 6 a. The first direction and the second direction are interchangeable, and are understood to be first direction wavelength channels in fig. 6a and second direction wavelength channels in fig. 9 a.
Taking the example that CH8, CH9, CH10, CH11 and CH12 are located in the ZDW region, the second-direction wavelength channels are distributed in the 8 th, 9 th and 12 th wavelength channels, and the three second-direction wavelength channels do not generate four-wave mixing; the first direction wavelength channels are distributed between the 10 th and 11 th wavelength channels, and the two first direction wavelength channels do not generate four-wave mixing. Moreover, the 6 first-direction wavelength channels satisfy: there are no four symmetric first direction wavelength channels centered in the ZDW region, nor are there: three first direction wavelength channels, equally spaced and at least two of which are located in the ZDW region. The 6 second direction wavelength channels satisfy: the center of the second direction wavelength channels where there are no four symmetries is located in the ZDW region, nor is there any: three second direction wavelength channels equally spaced and at least two of which are located in the ZDW region. It is also understood that the distribution of 6 first-direction wavelength channels and 6 first-direction wavelength channels based on the above-described scheme 4.1 satisfies the above-described condition 1 and condition 2. Thus, the distribution based on scheme 4.1 above helps to further attenuate or suppress the four-wave mixing effect.
It should be noted that, in the wavelength channel distribution in the above-mentioned scheme 4.1, four symmetrical first-direction wavelength channels exist in the N first-direction wavelength channels, that is, CH4, CH5, CH10, and CH11, and the centers of the four symmetrical first-direction wavelength channels are located between CH7 and CH8, so that the four-wave mixing effect is weak. Similarly, four symmetrical second-direction wavelength channels, namely CH2, CH3, CH8 and CH9, exist in the N second-direction wavelength channels, and the centers of the four symmetrical second-direction wavelength channels are positioned between CH5 and CH6, so that the four-wave mixing effect is weaker.
Scheme 4.2, the wavelength of the first direction wavelength channel is longer than the wavelength of the second direction wavelength channel.
Fig. 9b is a schematic diagram showing a distribution of wavelength channels according to another embodiment of the present application. The distribution diagram of the wavelength channels corresponds to the sequence number 50 in table 2. The 6 first direction wavelength channels and the 6 second direction wavelength channels are distributed in order from small to large: the second direction wavelength channel, the first direction wavelength channel, the second direction wavelength channel. Or may be expressed as a distribution of 6 first-direction wavelength channels: distribution mode of CH2-CH3-CH5-CH8-CH9-CH11,6 wavelength channels in the second direction: CH1-CH4-CH6-CH7-CH10-CH12. It will be appreciated that fig. 9b above corresponds to the first and second directions of CH3 and CH4, the first and second directions of CH5 and CH6, the first and second directions of CH9 and CH10, and the first and second directions of CH11 and CH12 of fig. 6b above.
The four-wave mixing effect of the optical fiber can be reduced or suppressed based on the distribution of the 6 first direction wavelength channels and the 6 second direction wavelength channels in the above-mentioned scheme 4.2, and the specific analysis can be described in the scheme 4.1, which is not repeated here.
It should be noted that, in the wavelength channel distribution in the above-mentioned scheme 4.2, four symmetrical second-direction wavelength channels exist in the 6 second-direction wavelength channels, that is, CH4, CH5, CH10, and CH11, and the centers of the four symmetrical second-direction wavelength channels are located between CH7 and CH8, and the interval is large, so that the four-wave mixing effect is weak. Similarly, four symmetrical first-direction wavelength channels exist in the N first-direction wavelength channels, namely CH2, CH3, CH8 and CH9, and the centers of the four symmetrical first-direction wavelength channels are positioned between CH5 and CH6, and the interval is larger, so that the four-wave mixing effect is weaker.
Transmission in the fiber through the above-described schemes 4,6 first-direction wavelength channels and 6 second-direction wavelength channels does not result in severe non-degenerate four-wave mixing (i.e., non-degenerate four-wave mixing). Theoretical simulations have found that based on the profile of this scheme 3, the performance degradation caused by four-wave mixing can be reduced by a factor of about 20 compared to the profile (configuration) of fig. 3. Further analysis of the effects can be found in the description of scheme 2 above, and will not be described in detail here.
It will be appreciated that the above-given distribution of wavelength channels that attenuate or suppress four-wave mixing is merely an example, and that any distribution of wavelength channels that may satisfy the above-described condition 1 and/or condition 2 and/or condition 3 and/or condition 4 may attenuate or suppress four-wave mixing. For example, the wavelength channel distribution of the number 7/15/18/39/46/50 in table 2 can also effectively reduce or suppress the four-wave mixing effect of the wavelength channels in the optical fiber.
2. First node and second node
In one possible implementation, the first node includes N first optical transceivers and one first combiner/divider, and a first end of the first combiner/divider is connected to the N first optical transceivers; the second node comprises N second optical transceivers and a second multiplexer/demultiplexer, and the first end of the second multiplexer/demultiplexer is connected with the N second optical transceivers. The second end of the first combiner/divider is connected to the optical fiber between the first node and the second node, and the second end of the second combiner/divider is connected to the optical fiber between the first node and the second node. In other words, the second end of the second combiner/divider and the second end of the second combiner/divider may be connected by a backbone fiber. In this way, only N first optical transceivers and N second optical transceivers are required to transmit 2N wavelength channels, which helps to reduce the number of first optical transceivers and/or the number of second optical transceivers included in the optical communication system.
Further, optionally, the number of ports at the first end and the second end of the first combiner/divider is N:1, the number of ports at the first end and the second end of the second multiplexer/demultiplexer is N:1. the N first direction wavelength channels are sent through the N ports of one first combiner/demultiplexer and the N second direction wavelength channels can be received, that is, the N ports of one first combiner/demultiplexer realize the transmission of 2N wavelength channels, which is helpful for the first combiner/demultiplexer to save 50% of the port number. Further, the N second direction wavelength channels are sent through the N ports of one second combiner/demultiplexer and the N first direction wavelength channels are received, that is, the N ports of one second combiner/demultiplexer realize transmission of 2N wavelength channels, which is helpful for the second combiner/demultiplexer to save 50% of the number of ports.
Illustratively, the number of ports at the first end of the first combiner/demultiplexer (or the second combiner/demultiplexer) is N, and the number of ports at the second end is 1; alternatively, the number of ports at the first end of the first combiner/divider (or the second combiner/divider) is n×n, N is an integer greater than 1, the number of ports at the second end is 2, and so on. It should be noted that, in order to prevent the first combiner/demultiplexer from being unable to be used normally due to a failure in the number of ports at one or several first ends, the number of ports at the first end of the first combiner/demultiplexer (or the second combiner/demultiplexer) may be any integer greater than N and less than nxn. Similarly, the second end of the first combiner/divider (or the second combiner/divider) may also include more than 2 ports.
Fig. 10 is a schematic diagram of a connection relationship between a first node and a second node according to the present application. In this example, n=6 is taken as an example. The first node includes 6 first optical transceivers and one first MUX/DMUX. Further, the first node may also comprise a DU/CU. The second node includes a second MUX/DMUX and 6 second optical transceivers. Further, optionally, the second node may further comprise 6 AAUs. The first end of the first MUX/DMUX is connected with 6 first optical transceivers, the second end of the first MUX/DMUX is connected with the second end of the second MUX/DMUX through a trunk optical fiber, the first end of the second MUX/DMUX can be connected with 6 second optical transceivers through 6 household optical fibers, and the 6 first optical transceivers are connected with DU/CU. The 6 second optical transceivers may be connected with the AAU.
It should be noted that the DU/CU, the first optical transceiver, and the first MUX/DMUX may be integrally integrated, or any two of them may be integrally integrated, or three independent physical entities may be also possible. The AAU may be integrally formed with the second optical transceiver or may be two separate physical entities.
In one possible implementation, one first optical transceiver corresponds to one first direction wavelength channel and one second direction wavelength channel, adjacent to the first direction wavelength channel and the second direction wavelength channel corresponding to the same first optical transceiver. Further, a second optical transceiver corresponds to a first direction wavelength channel and a second direction wavelength channel, adjacent to the first direction wavelength channel and the second direction wavelength channel corresponding to the same second optical transceiver. It is also understood that adjacent first-direction wavelength channels and second-direction wavelength channels are used for bidirectional transmission between the first node and the second node, one first optical transceiver corresponding to each wavelength channel pair and one second optical transceiver also corresponding to each wavelength channel pair. Alternatively, it is understood that the first optical transceiver is configured to transmit a first directional wavelength channel and to receive a second directional wavelength channel belonging to the same pair of wavelength channels. The second optical transceiver is configured to receive the first-direction wavelength channel and transmit a second-direction wavelength channel belonging to the same wavelength channel pair. Each of the first optical transceiver and the second optical transceiver is preconfigured with a corresponding first-direction wavelength channel and second-direction wavelength channel. The bidirectional transmission is realized through the single fiber, so that the number of the trunk optical fibers can be saved, and the number of the fiber to the home can be saved, thereby improving the resource utilization rate of the optical fibers.
Taking the above scheme 1.1 as an example, in the first direction: the DU/CU transmits CH1, CH3, CH5, CH7, CH9 and CH11 through 6 first optical transceivers, and after multiplexing through the first MUX, the DU/CU transmits the data on a main optical fiber, and after reaching a second MUX/DMUX, the data are respectively transmitted to corresponding second optical transceivers through de-multiplexing of the second DMUX, and are transmitted to a connected AAU through the second optical transceivers. In the second direction: the AAU transmits CH2, CH4, CH6, CH8, CH10 and CH12 through the second optical transceiver, multiplexes through the second MUX, transmits on the trunk optical fiber, reaches the first MUX/DMUX, demultiplexes through the first DMUX, and outputs to the DU/CU. The transmission process of the other schemes is not specifically listed here, and the distribution of the 6 first direction wavelength channels and the 6 second direction wavelength channels may be replaced by corresponding distribution schemes.
In one possible implementation, the first optical transceiver may be, for example, a first (Bi-directional, biDi) optical module (or referred to as a BiDi transceiver module, or referred to as a BiDi bidirectional transmission module), or may also be a first fiber circulator. The second optical transceiver may be, for example, a second BiDi optical module, or may also be a second fiber circulator. Further, alternatively, the first BiDi optical module and the second BiDi optical module may be identical, and may be collectively referred to as a BiDi optical module for convenience of the following description. The first and second fiber optic circulators may also be identical, and may be collectively referred to as fiber optic circulators for ease of description that follows.
The BiDi optical module is a bi-directional optical module, and has only one port, and filters through a filter in the BiDi module, so that the transmission of one wavelength channel and the reception of the other wavelength channel can be completed simultaneously. For example, the first node side transmits a 1310nm wavelength channel while receiving a 1330nm wavelength channel. The second node uses the wavelength channel exactly opposite to the first node side, i.e. transmits 1330nm wavelength channel and receives 1310nm wavelength channel.
Fig. 11 is a schematic structural view of an optical fiber circulator according to the present application. The optical fiber circulator can realize bidirectional transmission of the optical fiber side wavelength channel. The fiber optic circulator is a multi-port nonreciprocal optical device with wavelength channels that can propagate in only one direction. Illustratively, both receiving and transmitting are handled through two ports. If the wavelength channel 1 is input from the port 1, the wavelength channel is output from the port 2; if wavelength channel 2 is input from port 2, it will be output from port 3. If the wavelength channel 2 is input from the port 2, the loss is large when output from the port 1, and similarly, if the wavelength channel 1 is input from the port 3, the loss is large when output from the port 1 or the port 2. The optical fiber circulator has a simple structure, and can be connected with a DU/CU or an AAU by only one optical fiber connector, thereby being beneficial to reducing the volume of an optical communication system.
Referring to fig. 12, a schematic diagram of a connection relationship between a first optical fiber circulator and a second optical fiber circulator is provided in the present application. The first optical transceiver may include a first transmitting port and a first receiving port, the second optical transceiver may include a second transmitting port and a second receiving port, three ports of the first optical circulator are connected with the first transmitting port, the first receiving port and the second optical circulator, respectively, and three ports of the second optical circulator are connected with the second transmitting port, the second receiving port and the first optical circulator, respectively.
In various embodiments of the application, where no special description or logic conflict exists, the terms and/or descriptions between the various embodiments are consistent and may reference each other, and features of the various embodiments may be combined to form new embodiments based on their inherent logic relationships.
In the present application, "at least one" means one or more, and "a plurality" means two or more. "and/or", describes an association relationship of an association object, and indicates that there may be three relationships, for example, a and/or B, and may indicate: a alone, a and B together, and B alone, wherein a, B may be singular or plural. In the text description of the present application, the character "/", generally indicates that the front-rear associated object is an or relationship. In the formula of the present application, the character "/" indicates that the front and rear associated objects are a "division" relationship. In the application, the symbol "(a, b)" represents an open section, the range being greater than a and less than b; "[ a, b ]" means a closed interval in a range of greater than or equal to a and less than or equal to b; in addition, in the present application, the term "exemplary" is used to mean that the embodiment or design described as "example" in the present application should not be interpreted as being more preferable or advantageous than other embodiments or designs.
It will be appreciated that the various numbers referred to in this disclosure are merely for ease of description and are not intended to limit the scope of embodiments of the application. The sequence number of each process does not mean the sequence of the execution sequence, and the execution sequence of each process should be determined according to the function and the internal logic. The terms "first," "second," and the like, are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. Furthermore, the terms "comprising," "including," and "having," and variations thereof, are intended to cover a non-exclusive inclusion, such as a series of steps or elements. The method, system, article, or apparatus is not necessarily limited to those explicitly listed but may include other steps or elements not explicitly listed or inherent to such process, method, article, or apparatus.
Claims (23)
1. An optical communication system, comprising a first node, a second node, and an optical fiber for connecting the first node and the second node, wherein a zero dispersion wavelength ZDW of the optical fiber belongs to a ZDW region;
the optical fiber is configured to transmit N first direction wavelength channels and N second direction wavelength channels, where N is an integer greater than 2, at least two first direction wavelength channels and at least one second direction wavelength channel are located in the ZDW area, or at least two second direction wavelength channels and at least one first direction wavelength channel are located in the ZDW area, where the first direction wavelength channels and the second direction wavelength channels in the ZDW area are mixed and distributed, and the first direction wavelength channels are wavelength channels sent by the first node to the second node, and the second direction wavelength channels are wavelength channels sent by the second node to the first node.
2. The system of claim 1, wherein the N first direction wavelength channels and the N second direction wavelength channels are distributed to satisfy any one or more of the following:
among the N first-direction wavelength channels, there are no: the centers of the four symmetrical first-direction wavelength channels are positioned in the ZDW area;
among the N second-direction wavelength channels, there are no: the centers of the four symmetrical second-direction wavelength channels are located in the ZDW region.
3. The system of claim 1 or 2, wherein the N first direction wavelength channels and the N second direction wavelength channels are distributed to satisfy any one or more of the following:
among the N first-direction wavelength channels, there are no: three first-direction wavelength channels equally spaced and at least two of which are located in the ZDW region;
among the N second-direction wavelength channels, there are no: three second direction wavelength channels equally spaced and at least two of which are located in the ZDW region.
4. A system according to any one of claims 1 to 3, wherein the minimum frequency separation of the N first direction wavelength channels and the N second direction wavelength channels of the hybrid distribution is equal to 800 gigahertz.
5. A system according to any one of claims 1 to 3, wherein the minimum frequency separation of the N first direction wavelength channels and the N second direction wavelength channels of the hybrid distribution is equal to 400 gigahertz.
6. The system of any one of claims 1-5, wherein the N first direction wavelength channels have the same wavelength spacing and the N second direction wavelength channels have the same wavelength spacing.
7. The system of claim 6, wherein N = 6;
the N first direction wavelength channels and the N second direction wavelength channels are distributed in order from small wavelength to large wavelength:
a first directional wavelength channel, a second directional wavelength channel, a first directional wavelength channel, a second directional wavelength channel; or,
the second direction wavelength channel, the first direction wavelength channel, the second direction wavelength channel, the first direction wavelength channel.
8. The system of any one of claims 1-5, wherein the N first direction wavelength channels have different wavelength intervals; and/or, the wavelength intervals of the N second direction wavelength channels are different.
9. The system of claim 8, wherein N = 6;
the N first direction wavelength channels and the N second direction wavelength channels are distributed in order from small wavelength to large wavelength:
a first directional wavelength channel, a second directional wavelength channel, a first directional wavelength channel, a second directional wavelength channel; or,
a second direction wavelength channel, a first direction wavelength channel, a second direction wavelength channel, a first direction wavelength channel the first direction wavelength channel, the second direction wavelength channel, the first direction wavelength channel.
10. The system of claim 8, wherein N = 6;
the N first direction wavelength channels and the N second direction wavelength channels are distributed in order from small wavelength to large wavelength:
a first directional wavelength channel, a second directional wavelength channel, a first directional wavelength channel, a second directional wavelength channel, a first directional wavelength channel, a second directional wavelength channel; or,
the second direction wavelength channel, the first direction wavelength channel, the second direction wavelength channel, the first direction wavelength channel.
11. The system of claim 8, wherein N = 6;
the N first direction wavelength channels and the N second direction wavelength channels are distributed in order from small wavelength to large wavelength:
A first directional wavelength channel, a second directional wavelength channel, a first directional wavelength channel, a second directional wavelength channel, a first directional wavelength channel; or,
the second direction wavelength channel, the first direction wavelength channel, the second direction wavelength channel.
12. The system according to any one of claims 7, 9-11, wherein the longest 5 of the 6 first direction wavelength channels and the 6 second direction wavelength channels of the mixed distribution are located in the ZDW region.
13. The system of any one of claims 1-12, wherein the optical fiber comprises a standard single mode fiber having a ZDW region in the range of [1300 nm, 1324 nm ].
14. The system of any of claims 1-13, wherein the first node comprises N first optical transceivers and a first combiner/divider, and the second node comprises N second optical transceivers and a second combiner/divider;
the first ends of the first optical combiners are connected with the N first optical transceivers, and the second ends of the first optical combiners are connected with optical fibers between the first nodes and the second nodes;
the first ends of the second optical combiners are connected with the N second optical transceivers, and the second ends of the second optical combiners are connected with optical fibers between the first nodes and the second nodes.
15. The system of claim 14, wherein a first optical transceiver corresponds to a first directional wavelength channel and a second directional wavelength channel, adjacent to the first directional wavelength channel and the second directional wavelength channel corresponding to the same first optical transceiver; and/or the number of the groups of groups,
a second optical transceiver corresponds to a first direction wavelength channel and a second direction wavelength channel, adjacent to the first direction wavelength channel and the second direction wavelength channel corresponding to the same second optical transceiver.
16. The system of claim 14 or 15, wherein the first optical transceiver comprises a first fiber optic circulator and the second optical transceiver comprises a second fiber optic circulator.
17. The system of any of claims 14-16, wherein the first and second ends of the first combiner/divider have a number of ports N:1, the number of ports at the first end and the second end of the second multiplexer/demultiplexer is N:1, wherein N is a positive integer.
18. The system according to any of the claims 1-17, wherein the first node comprises a distribution unit DU and/or a central unit CU and the second node comprises an active antenna unit AAU.
19. A first node, comprising:
n first optical transceivers for transmitting N first direction wavelength channels and for receiving N second direction wavelength channels, the N being an integer greater than 2;
the N first direction wavelength channels and the N second direction wavelength channels are transmitted through an optical fiber, the zero dispersion wavelength ZDW of the optical fiber belongs to a ZDW area, at least two first direction wavelength channels or at least two second direction wavelength channels are located in the ZDW area, the first direction wavelength channels and the second direction wavelength channels in the ZDW area are mixed and distributed, the first direction wavelength channels are wavelength channels sent by the first node to the second node, and the second direction wavelength channels are wavelength channels sent by the second node to the first node.
20. The node of claim 19, wherein the first node further comprises a first combiner/divider, a first end of the first combiner/divider being coupled to the N first optical transceivers, a second end of the first combiner/divider being configured to be coupled to the optical fibers.
21. A node according to claim 19 or 20, wherein a first optical transceiver corresponds to a first directional wavelength channel and a second directional wavelength channel, adjacent to the first directional wavelength channel and the second directional wavelength channel corresponding to the same first optical transceiver.
22. The node of any of claims 19-21, wherein the first optical transceiver comprises a first fiber optic circulator.
23. The node according to any of claims 20-22, wherein the number of ports at the first end and the second end of the first combiner/divider is N:1.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210275920.9A CN116827438A (en) | 2022-03-21 | 2022-03-21 | Optical communication system and first node |
| PCT/CN2023/082914 WO2023179630A1 (en) | 2022-03-21 | 2023-03-21 | Optical communication system and first node |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202210275920.9A CN116827438A (en) | 2022-03-21 | 2022-03-21 | Optical communication system and first node |
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| JPH11186969A (en) * | 1997-12-17 | 1999-07-09 | Nippon Telegr & Teleph Corp <Ntt> | Optical transmission system |
| JP3370949B2 (en) * | 1998-04-22 | 2003-01-27 | 日本電信電話株式会社 | Wavelength allocation method, transmission device using the method, and wavelength division multiplexing transmission system |
| US8260138B2 (en) * | 2008-04-07 | 2012-09-04 | Arris Solutions, Inc. | Wavelength distribution for optical transport |
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